1. Field of the Invention
This invention relates to chewing gum compositions and methods utilizing same which are useful to remineralize subsurface dental enamel. More specifically, this invention relates to stable, single-part chewing gum compositions containing calcium and phosphate salts which when applied to lesions in dental enamel result in remineralization of subsurface dental enamel and/or mineralization of tubules in dentin thereby counteracting caries and/or hypersensitivity.
2. The Prior Art
The primary component of the enamel and dentin in teeth is calcium phosphate in the form of calcium hydroxyapatite. This material highly insoluble at normal oral pHs. However, carious lesions form in teeth, when they are subjected to acids produced from the glycolysis of sugars by the action of various oral bacteria. This is because calcium phosphate salts are more soluble in acidic media.
Saliva is supersaturated with respect to calcium and phosphate ions. Saliva therefore helps protect teeth against demineralization and can slowly remineralize teeth which have become demineralized by acids. It is well known that the presence of fluoride ions can enhance the natural remineralization process and this is one of the accepted mechanisms by which fluoride toothpastes and rinses protect against caries. The efficacy of fluoride containing toothpastes and rinses to remineralize teeth is limited by the modest levels of calcium and phosphate in saliva. It is evident from the prior art that it is highly desirable to increase the available concentration of calcium and phosphate ions in the oral cavity to speed up the remineralization process. However, because of calcium phosphate's low solubility at the pH of saliva the addition of higher levels of dissolved calcium and phosphate ions is not easily accomplished.
Remineralization of dental enamel has been carried out experimentally both in vivo and in vitro. Some studies have concentrated on the remineralizing properties of saliva and synthetic solutions supersaturated with respect of hydroxyapatite. Such studies comprise the subject matter of U.S. Pat. Nos. 3,679,360 (Rubin) and 4,097,935 (Jarcho).
Generally, the supersaturated solutions or slurries used in these patents for remineralization experiments have been prepared from a single form of calcium phosphate. When a carious lesion is flooded with one of these supersaturated solutions, the calcium and phosphate ions in the form of precipitated hydroxyapatite remineralize the lesion.
However, these solutions are impractical for use for several reasons. First, the amount of calcium and phosphate ions available for remineralization in these supersaturated solutions is too low. It is reported that it takes approximately 10,000 unit volumes of the usual supersaturated solution to produce one unit volume of mineral. Thus, remineralization by this method requires both an excessive volume of fluid and an excessive number of applications. The supersaturated solutions are inherently limited in this respect because they cannot maintain their supersaturated state. When the hydroxyapatite precipitates out to the point where the solution is no longer supersaturated, new supersaturated solution must be introduced or the remineralization process stops.
Another problem with single calcium phosphate slurries is that as the hydroxyapatite precipitates out of solution, the pH of the solution changes. Unless the old solution is removed from contact with the tooth material, the solution may become too acidic or alkaline and damage the dental tissue.
U.S. Pat. Nos. 4,083,955 (Grabenstetter et al) and 4,397,837 (Raaf et al) provide processes utilizing various dentifrices, including chewing gums, for remineralizing demineralized enamel by the consecutive treatment of tooth surfaces with separate solutions containing calcium ions and phosphate ions. Fluoride ions may be present in the phosphate solutions. It is immaterial which ionic solution is used to treat the teeth first. By sequentially applying calcium and phosphate ions to the tooth surface high concentrations of the ions are able to diffuse or penetrate into lesions in solution form, where they precipitate as a calcium phosphate salt when ions from the second treatment solution diffuse in. While apparently successful this method involves the inconvenience of employing two different chewing portions, one containing the calcium ions and the other the phosphate ions. This method could be confusing because of the necessity of ensuring the proper sequence of gum portions and also inconvenient due to the plurality of sequential applications which can be found to be time consuming.
U.S. Pat. Nos. 5,037,639 and 5,268,167 (Tung) involve the use of amorphous calcium compounds such as: amorphous calcium phosphate (ACP), amorphous calcium phosphate fluoride (ACPF) and amorphous calcium carbonate phosphate (ACCP) for use in remineralizing teeth. These amorphous compounds or solutions which form the amorphous compounds when applied either onto or into dental tissue prevent and/or repair dental weaknesses such as dental caries, exposed roots and dentin sensitivity. The compounds are claimed to have high solubilities, fast formation rates and fast conversion rates (to apatite).
Remineralization is accomplished by bringing the amorphous compound into contact with the dental tissue. This can be done directly, i.e., putting an amorphous compound directly on the tooth, or indirectly through a carrier, i.e., incorporating the amorphous compound in a carrier such as a gel, a chewing gum, or a toothpaste and applying the carrier to the dental tissue. Once contact is established with the tooth, the amorphous calcium phosphate compounds will recrystalize to the less soluble apatite form in the lesion and reform the tooth. However, under conditions where amorphous calcium phosphate compounds are stable, the quantity of calcium and phosphate released is relatively low and, therefore, remineralization is slower than desirable.
International Patent WO 94/18938 (Greenberg) adds calcium glycerophosphate to a chewing gum. The calcium glycerophosphate is said to increase calcium and phosphate concentrations in plaque, increasing remineralization and decreasing demineralization. It may also inhibit large drops in pH in plaque and interfere with metabolism of S. mutans. A problem with this technology is that the glycerophosphate ion has to hydrolyze and release free phosphate ions before it can participate in the remineralization process. Hydrolysis occurs in the mouth due to the presence of phosphatase enzymes. However, the process is slow. The high concentration of calcium ions supplied by the calcium glycerophosphate therefore have time to dissipate before sufficient phosphate can be released to produce maximum remineralization.
Thus, the problem with known remineralization compositions and techniques is that there is not a one-part, stable remineralizing composition that may be suitably prepared as a chewing gum and the like which is not negatively affected by a rise in pH or temperatures or which can efficiently remineralize teeth.
There is a need for a method of remineralizing dental enamel which employes a stable, single-part remineralizing chewing gum composition which does not require excessive amounts of calcium and phosphate salts and inordinately long, frequent or sequential exposure times.
It is the object of the present invention to provide a single-part stable chewing gum composition and method for the remineralization and the prevention of demineralization of human teeth, which chewing gum composition and the use thereof are capable of effectively incorporating calcium ions, phosphate ions and, if desired, fluoride ions into the dental enamel, the chewing gum composition also being easily usable by the consumer and not differing significantly, in flavor and appearance, from customary chewing gums.